Monday, January 11, 2016

Climate Science's Climate Change Model

In this series of blog posts, I attempt to give an overall
view of the physics/chemistry-based climate science dealing with climate change
and today’s global warming.I do so
because I can’t find an overall summary such as the one I’m about to try to
create.My hope is that readers will
understand why this science makes me so alarmed and seemingly so
pessimistic.As always,
misunderstandings and misstatements are my fault and do not reflect on the
science itself.

Let’s begin with sunlight.The sun’s light is always accompanied by warmth/energy.Even on barren Mars, without an atmosphere to
“contain” that warmth, temperatures at the surface are 100 degrees F below
zero, only part of which is due to the planet’s internal heat.The rest is sunlight striking the surface
during daylight and giving off heat that is absorbed and radiated by surface
materials.

The actual amount of absorption and heating depends on the
“color” of the surface (or, in scientific jargon, the “albedo” of materials).More specifically, think of the color
spectrum you were taught:white reflects
all (except perhaps infrared) radiation, and absorbs no or very little heat.Black absorbs all (except perhaps
ultraviolet) radiation, and therefore absorbs a lot of heat.On the Earth, water is blue and absorbs a
moderate amount of heat; ice and snow are white or off-white and absorb very
little heat; and soil and rock tend to be brown and black and absorb lots of
heat.Likewise, land covered by
vegetation tends to be light to dark green and absorbs much more heat than the
sand that would otherwise predominate on land – and that doesn’t even consider
the effects of photosynthesis.

Finally, the atmosphere of Earth takes reflected light and
reflects it back to Earth, adding yet more warmth.The amount reflected depends on the amount of
certain elements in the atmosphere.

The warmth of Earth therefore consists of three layers,
added over time:

1.Light striking the surface of the planet,
heating it to perhaps -100 degrees F;

2.The atmosphere that both reflects some light
back to the surface and prevents water from evaporating into space – resulting
in oceans that absorb more light/heat, raising the temperature to perhaps -30
degrees F; and

3.Animal and vegetative (plant) matter, both dead
and alive, that absorb still more light/heat and raise the global average
temperature to 56 degrees F – in a “steady state” climate.

Carbon Dioxide and Other So-Called “Greenhouse Gases”

“Greenhouse” is a misleading term for what these gases do,
which is to reflect light from other parts of the spectrum than are handled by
oxygen and hydrogen (the main components of the atmosphere). However, compared to oxygen and hydrogen, these
can vary much more over long periods of time.In the case of carbon, a “steady-state” value is about 250 ppm, but
historically carbon has been above 1000 ppm and below 200 ppm at various
times.Carbon is one of six elements in the periodic table that is
constantly cycling between the atmosphere and the surface of the planet.Life forms are carbon-based, so animals and
vegetables (in the sea as well) constantly add carbon that is either buried as
part of the animal/vegetable fossil, or released to the air via breathing or
burning (in the case of forests).However, in order for the amount in the atmosphere and the surface of
the Earth to roughly balance, carbon must also be absorbed by “weathering”,
wind/rain erosion of rocks that exposes new rock with which carbon can combine.These are usually eventually washed down to
the oceans, which equalize with the atmosphere by agitation that propels the
carbon into the air.In essence, then,
over the long run this cycling stabilizes carbon in the atmosphere at about 250
ppm. The “half-life” of carbon in the
atmosphere is about 100 years, so if no cycling upwards were going on it would
take about 200 years to drain the atmosphere of carbon.

Probably the only other “greenhouse gas” relevant to climate
is methane, which is CH4.Without me
going into a long discussion of methane, you should know that it, too, has seen
a massive upsurge in emissions over the last 165 years due to human
emissions.However, the half-life of
methane is about 9 years, and the amount of emitted methane needed to have an
impact on global temperature comparable to carbon is about 4-10 times what is
presently being emitted per year, while the amount unlockable in shallow waters
or permafrost in any given 9 years, even at our accelerated pace of warming, is
probably less than that.Rather, because
methane contains carbon, the long-term worry is the possibility that the
methane in permafrost will be converted primarily to carbon, which would add
about 0.6C (guesstimate) to hundreds-of-years global warming.

Plate Tectonics and the Milankovitch Cycle

There are two main ways that atmospheric carbon can deviate
significantly from the norm, absent human intervention.One is predictable, cyclic variation over a
period of 100,000 to 200,000 years:the
Milankovitch cycle.The other is
underwater volcanism that ejects carbon, typically while moving one of the
Earth’s plates.

The Milankovitch cycle results from three changes in the
Earth’s orbit around the Sun:

1.The Earth
wobbles around its axis of spin;

2.The Earth’s orbit at some times of the year
takes it closer to the Sun, at others further away;

3.Like a rubber band, the Earth’s yearly orbit
sometimes becomes more like a circle, sometimes more like an ellipse.

Visualize these in your mind.At about the point where it is winter in the
Northern Hemisphere (where most of the land is) and where the other two effects
place the Earth farthest from the Sun, an ice age is kick-started.The temperature descends gradually as ice
encroaches downwards from the Arctic Ocean over land, changing the albedo in
the areas affected.Less carbon is
exposed, and so less carbon is emitted into the atmosphere.This continues until the three effects are
closest to the Sun, in Northern Hemisphere’s summer, when a pretty rapid rise in
temperature and carbon occurs, reaching a steady state that lasts for about
50-100,000 years.

The underwater volcanism effect is much less frequent but
can be far more powerful in its effect on atmospheric carbon and global
warming.In the most recent example, about
55 million years ago, continuous underwater eruptions in around the plate then
near the South Pole sent it steadily northwards to crash into the Eurasia
plates, yielding India plus the Himalayas at the point of impact.During this period, which is unlikely to have
lasted less than 20,000 years, steady output of carbon into the atmosphere kept
the atmospheric carbon above 1000 ppm.The
results were high temperatures (about 7 degrees C more than the present time),
mass extinctions of land and sea flora and fauna, and very high sea levels –
so-called “hell and high water.”Mass
extinctions, high temperatures, and high sea levels have also been confirmed
for the previous such atmospheric-carbon rise (about 155 million years ago).

Also noteworthy is what happened after the eruptions came to
an end.Atmospheric carbon decreased
back to its “steady-state” level, but only slowly.In the case of the most recent such episode,
atmospheric carbon took 50-54 million years to return to “steady-state”,
reaching it only 1-5 million years ago.The reason is that the oceans were in effect saturated with carbon:most of any decrease in atmospheric carbon
was offset by fresh contributions from the ocean, while “weathering” that
returned the carbon to the planet’s interior worked only slowly to end that
saturation.

And another factor worthy of note is the composition of the carbon
dioxide.Carbon dioxide put in the air
during one of these extraordinary periods is more acid than “normal” CO2.Therefore, the atmosphere and rain are both
more acid than in “steady-state” periods.

Summary

The Earth’s climate can therefore be said to be a process
that operates to keep climate relatively stable both in the short (10,000s of
years) and long (billions of years) term, but where too large a deviation from
atmospheric carbon stability has the opposite effect:it drives and maintains further deviation to
a new “semi-steady state” that lingers for a while even when the main impetus
for deviation is gone.To cite one
example:we are presently in the late
stages of the “high-temperature” phase of the Milankovitch cycle; what some
scientists call the “Goldilocks” climate (not too hot nor too cold for human
purposes).Absent human-caused carbon
emissions, we would have expected to see a slow descent into an Ice Age begin
in less than 10,000 years.

The critical factor in creating both Milankovitch and
plate-tectonic deviations from a “Goldilocks” steady state is atmospheric
carbon.In the case of the Milankovitch
cycle, increased/decreased sunlight is the initial cause of warming/cooling,
followed by a feedback loop between sunlight absorption and carbon
emissions.In the case of underwater
volcanism, the atmospheric carbon itself is the initial cause of warming,
followed by a feedback loop between sunlight absorption and carbon emissions as
well as further volcanic carbon injections.

A minor note:Above a
certain point, atmospheric carbon would become so prevalent as to drive global
temperatures above the boiling point of water.The oceans would then evaporate, and from then on global surface temperatures
would be such that acid (from the carbon) rain would simply evaporate before it
reaches the surface, and no life apparently could survive.The planet Venus now operates in just such a
way.Luckily, even if all fossil-fuel
reserves were used, we cannot presently reach that point of atmospheric
carbon.However, heat from the sun
increases at the rate of 1 degree C every billion years, and therefore, at the
earliest, it would be possible for Earth to turn into Venus 900 million years
from now.

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Wayne Kernochan

About Me

I have recently retired. Before retirement, I was a long-time computer industry analyst at firms like Aberdeen Group and Yankee Group, and before that a programmer at Prime Computer and Computer Corp. of America. Sloan/MIT MBA, Cornell Computer Science Master's, and Harvard college degrees. Used to play the violin, and have written unpublished books about personal finance, violin playing, and the relationship between religion and mathematics, as well as three plays, two musicals, a screenplay on climate change, short stories, and poetry. I intend to use this blog in future both to continue to enjoy the computing field and to pursue my interests in many other areas (e.g., climate change, history, issues of the day).